Leave symbols in even on release builds

Ignore-this: b4d9b0728d1cde913b73c1b558c92aa8

darcs-hash:20140822142040-56b4d-be6421e59d6c0f47941ba007a1828cbcacd93731
Refactor initialization

Ignore-this: deb555a0f6838145819bd515782244a6

Initialize the Engine on it's own thread. Also create the PJSIPUA instance in that thread,
thus simplifying the Enigne.start() inplementation.

darcs-hash:20140825145957-56b4d-1e89aa587d093a8b1296de91068910f8bba3b967
pjsip: updated bundled PJSIP to revision 4818

Ignore-this: a0bc5220d0971f3b4ec15edb8d403e13

darcs-hash:20140416095122-56b4d-bc9591619d1954127d9575066bb37f12d12479f1